1. Field of the Invention
The present invention relates to a sheet feeding device and method for pneumatically floating sheets to be picked up one by one from a sheet stack and feeding the sheets into a transportation path, and the invention also relates to an image forming apparatus including the sheet feeding device.
2. Description of Related Art
As an invention relevant to a conventional sheet feeding device, for example, a sheet feeding device described in Japanese Patent Laid-Open Publication No. 2010-254462 is known. FIG. 15 is a configuration diagram of the sheet feeding device 100 described in Japanese Patent Laid-Open Publication No. 2010-254462.
The sheet feeding device 100 includes a blowing unit 102 that blows floating air onto the top edge of a stack of sheets Se (on the positive side in the z-axis direction), thereby floating the top sheet S1. Endless suction belts 104 with a number of through-holes provided therein are positioned above the stack of sheets Se. By means of an internal fan provided in a chamber (not shown) positioned inside relative to the suction belts 104, the top sheet is attracted to the suction belts 104 by drawing air between the stack of sheets Se and the suction belts 104 into the chamber via the through-holes. The suction belts 104 are rotated by a drive force from a motor (not shown). Accordingly, the attracted sheet is carried in the x-axis direction to a receiving port 108 of a transportation path 106. Thereafter, the top sheet S1 is carried through the transportation path 106 to an imaging unit (not shown).
The sheet feeding device 100 further includes an image pickup unit 110 and a control circuit 112. The image pickup unit 110 captures images of the floated top sheet S1 and another sheet immediately therebelow, from a predetermined distance in the y-axis direction relative to one side P1 of the stack of sheets Se. The control circuit 112 calculates the gap between the sheets on the basis of the images captured by the image pickup unit 110. Moreover, the control circuit 112 adjusts the volume of air from the blowing unit 102 on the basis of the calculated gap between the sheets.
Incidentally, the sheet feeding device 100 has difficulty in reliably separating the sheet S1 from the sheet immediately therebelow. More specifically, to separate the sheet S1 from the sheet immediately therebelow, the sheet feeding device 100 blows separation air between the sheets.
However, when the sheet S1 and the sheet immediately therebelow are in close contact with each other while being attracted to the suction belts 104, there is no gap between the sheets. Accordingly, the sheet feeding device 100 might not be able to separate the sheet S1 from the sheet immediately therebelow by blowing separation air to the sheets.